In a general conveyor machine or a machine tool, as means for reciprocatingly and linearly move a movable body such as a table, there is known a so-called linear motor actuator using a linear motor as a thrust force generation source. As the most general linear motor actuator, there is known one in which the movable body is supported by using a pair of linear guides on a stationary portion such as a bed or a column so as to be reciprocatingly movable, and a stator and a movable element constituting the linear motor are mounted so as to oppose to each other onto the stationary portion and the movable body, respectively (JP 10-290560 A or the like). Specifically, while track rails of the linear guides are arranged on the stationary portion and the stator of the linear motor is mounted thereonto in parallel to the track rails, sliders of the linear guides and a mover of the linear motor are mounted onto the movable body and the sliders on the movable body side are assembled to the track rail. As a result, the movable body is supported so as to be reciprocatingly movable on the stationary portion, and the stator on the stationary portion side and the mover on the movable body side are opposed to each other.
As the linear motor, there exist those of various types based on differences in their drive systems. As a representative one, there is provided the so-called linear synchronous motor, in which alternating currents of a plurality of phases pass through a coil to be used (JP 2003-070226 A, JP 08-205514 A, and the like). The linear synchronous motor includes a stator magnet having N poles and S poles alternately linearly arranged to generate a magnetic field, and a mover for generating a shifting magnetic field along an arrangement direction of the magnetic poles of the stator magnet by virtue of passage of the alternating current. Between the shifting magnetic field generated by the mover and the magnetic field generated by the stator magnet, a magnetic attractive force or a magnetic repulsive force is generated. As a result, a thrust force for relatively moving the mover and the stator magnet is generated.
There are two types of movers including and not including a core member made of a ferromagnetic material such as iron. The former type is advantageous in terms of an amount of thrust force to be generated. To the core member, teeth, the number of which is a whole-number multiple of the number of phases of the alternating current, are provided so as to oppose to the stator magnet. The coil is wound around those teeth. When the coil is electrified, each of the teeth becomes an electromagnet, and between the coil and the respective magnetic poles each constituting the stator magnet, the magnetic attractive force or the magnetic repulsive force is generated. For example, a three-phase alternating current is formed of three alternating currents consisting of a u phase, a v phase, and a w phase, having a phase difference of 120 degrees to each other. Accordingly, if the alternating currents having the phase difference of 120 degrees to each other are allowed to successively pass through the coil wound around a series of the teeth, in such a manner that the u-phase is at one end of the core member, the v-phase is at the next tooth, and the w-phase is at the tooth next to the next tooth, there occurs a phenomenon as if the magnetic field moves from the tooth positioned at one end of the core member toward the tooth positioned at the other end thereof. This is the above-mentioned shifting magnetic field. Owing to cooperation between the shifting magnetic field and the stator magnet, the thrust force acts between the mover and the stator magnet.    Patent Document 1: JP 10-290560 A    Patent Document 2: JP 2003-070226 A    Patent Document 3: JP 08-205514 A